1. Field of the Invention
The field of the invention is that of onboard equipment for aircraft and its control. In the field of aeronautics and, in particular, in the field of helicopters, the weight of onboard equipment is a critical factor insofar as it conditions the performance of the aircraft. Airplane and helicopter operators are therefore very sensitive to the gains in weight and volume that are able to be made on avionics equipment. These gains allow the useful load of the carrier, and hence its commercial value, to be increased.
2. Description of the Prior Art
The continued objective of avionics designers is therefore to design avionics systems with a high degree of integration in order to reduce the weight and the overall size without degrading the safety and security of operation and the functional and operational capacities of the equipment proposed.
The present invention relates to the control of a unit of equipment called “AHRS”, an acronym signifying “Attitude and Heading Reference System”. The function of the AHRS is to supply the attitude and heading parameters to the display screens and to the automatic pilot. Conventionally, the AHRS incorporates three gyroscopes, three accelerometers and also a magnetic compass. The magnetic compass supplies the heading of the carrier. The gyroscopes and the accelerometers supply the attitude parameters. In its normal mode of operation, the AHRS uses the magnetometer to supply the heading information. This mode of the AHRS is referred to as “SLAVE” mode: in other words, it is feedback controlled onto the magnetic compass. However, close to the earth's poles or near to sources of interference such as oil rigs, the magnetic heading is virtually useless since it is severely affected by the earth's magnetic field. In this case, the AHRS has a mode known as “DG”, for “Directional Gyro”, in which the AHRS calculates a heading, no longer based on the magnetic sensor but on an integration function of the gyroscopic accelerations. In order to use this mode correctly, the pilot has to manually input a heading which will be used as an initialization value for the integration calculation of the measurements coming from the gyroscopes of the AHRS.
In the same way, in the case of loss of the magnetometer sensor, the pilot can manually select the DG mode of the AHRS in order to have available the heading information supplied by the gyroscopes, once initialized by the pilot. In order to select the AHRS mode (DG or SLAVE) or to allow the pilot to correct the DG heading, the AHRS manufacturers offer dedicated control panels. Since the civil regulations impose a redundancy on this primary sensor, two AHRS units are disposed in the aircraft and two control panels are installed, dedicated to each AHRS. These two panels generate extra weight and take up space in the central part of the cockpit.
In order to gain in weight, some helicopter operators replace these control panels by buttons or control knobs directly installed in the cockpit. In this case, a gain in weight is achieved but the problem of cockpit congestion still remains.
Beyond the problems of congestion and performance, ergonomic issues associated with the existing mechanical interfaces still remain. The heading correction is still applied by means of a control knob which, depending on the direction in which the pilot turns it and depending on the amount of rotation he applies to it, supplies the AHRS, rather than with the raw value of initialization heading, with the rate at which the AHRS must modify the latest heading used. This rate can vary from 2 degrees/second to 8 degrees/second as a general rule. When the correction to be applied is significant, the action of the pilot will therefore be lengthy and necessarily iterative.